Household appliance comprising a first air conduit and a heat pump

ABSTRACT

A household appliance including a housing; a drying chamber to dry wet articles in the drying chamber; and a first air conduit to guide process air drawn into the housing to dry the wet articles. The household appliance also has a heat pump that includes a heat sink to transfer heat into the heat pump; a heat source coupled to the first air conduit to transfer the heat from the heat pump into the process air; and a heat transfer device to transfer the heat from the heat sink to the heat source. A second air conduit is coupled to the heat sink to guide secondary air drawn into the housing. The heat sink transfers the heat from the secondary air into the heat pump.

The invention relates to a household appliance comprising a housing, adrying chamber for drying wet articles therein, a first air conduit forguiding process air drawn into said housing to dry the articles and aheat pump, said heat pump comprising a heat sink for transferring heatinto said heat pump, a heat source coupled to said first air conduit fortransferring heat from said heat pump into the process air, and a heattransfer device for transferring heat from said heat sink to said heatsource.

A household appliance of this type is apparent from an abstract relatedto Japanese publication JP 2004 089 415 A and contained in the databasePatent Abstracts of Japan.

A household appliance for drying wet articles and comprising a heat pumpis apparent from EP 0 467 188 B1. That document contains a detaileddescription of a household appliance that is configured as a dryer fordrying articles which are wet laundry. The document refers to manydetails of the household appliance that may be necessary or at any rateadvantageous in making or using the appliance. Accordingly, the wholecontent of this document is incorporated herein by reference.

Related art for household appliances is apparent from documents WO2006/029953 A1 that specifies a dishwasher in relation to a laundrydryer or combined laundry washer and dryer, DE 197 38 735 C2 thatdiscloses a household appliance with a different type of heat pump, EP 1672 294 A2, and EP 1 672 295 A2, the latter two disclosing airconditioning devices that have cooling circuits which are in someaspects similar to the certain heat pumps considered herein.

Drying of wet articles in a household appliance generally requiresevaporating the humidity on the articles and transporting evaporate thusformed away by means of a current of heated process air. Such processair loaded with evaporate may be discharged from the appliance, orsubjected to a condensation process to recover the humidity from theevaporate in liquid form for collection and disposal. Such condensationprocess in turn requires cooling the process air, thereby extractingheat. That heat may again be discharged from the appliance simply. Inorder to keep consumption of energy low however, it may be desired torecover that heat at least to an extent. To that end, a householdappliance has been developed that incorporates a heat pump whichrecovers energy taken from the process air. To that end, the heat pumpcomprises a heat sink which is applied to cool the process air with thehumidity contained therein, thereby extracting heat from the processair. In addition, the heat pump comprises a heat source which is appliedto heat the process air prior to conveying it to the articles to bedried for pickup of humidity. Finally, the heat pump comprises a heattransfer device to transfer heat from the heat sink to the heat source,thereby accomplishing the desired recovery of heat.

In an exemplary heat pump that is also known from the documents referredto above, the heat transfer device comprises a heat transfer loop thatcontains a heat transfer agent or refrigerant that is circulated throughthe heat sink and the heat source repeatedly. The heat pump is operatedby evaporating the heat transfer fluid in the heat sink by heatextracted from process air flowing through, subsequently compressingthat heat transfer fluid and releasing heat from it back into theprocess air at the heat source. That release of heat makes the gaseousheat transfer fluid condensate or liquefy. The liquefied heat transferfluid is guided through a nozzle to reduce its internal pressure, and isfinally guided back to the heat sink for another evaporation and pickupof heat. The process air is generally kept in a substantially closedcircuit or process air loop except for the appliance known from the saidabstract relating to JP 2004 089 415 A, where the process air is guidedthrough an open cycle. While it may be expedient or even required toopen a closed process air loop at least occasionally as described in EP0 467 188 B1, pertinent IEC standards require that a dryer that isclaimed to recover humidity by condensation keeps any leakage ofhumidity below 20% of the total humidity present. Problems still to beencountered with such household appliances incorporating heat pumps arehigh manufacturing costs, relatively long periods needed to dryconvenient charges of laundry or the like, and possible environmentalhazards from heat transfer fluids applied in such appliances. Tomitigate such hazards that are predominantly related to ozone-destroyingor greenhouse effect enhancing properties, or flammability, of suchcompounds, chlorinated hydrocarbons that had been applied frequently inthe past are presently prohibited from use due to pertinent legislation.To allow quantitative assessment of greenhouse effect potentials ofusual refrigerants, a reference index named “Global Warming Potential”(“GWP index” in short hereinafter) has been assigned to each commonlyknown or used refrigerant, with carbon dioxide or R744 having its GWPindex defined to be equal to 1.

The pickup of humidity from articles to be dried by process air is onlyeffective if the process air is heated over any normal ambienttemperature, preferably to a temperature higher than 60° C. Thattemperature will be brought down by the evaporation process to asomewhat lower temperature. At any rate, a temperature around or above35° C. at an inlet of an evaporator heat exchanger may be expected topose a problem to a heat pump applying a heat transfer fluid asspecified above and designed in accordance with practice common in theart of refrigeration, in that compressors and refrigerant fluids(generally specified as “heat transfer fluids” herein) from normalrefrigeration practice are not suitable for the purpose. It has beenconsidered to obtain relief by reverting to refrigerants of remarkablyhigh critical temperatures so as to ascertain their function at workingtemperatures up to 60° C., but no thorough analysis and guidance isavailable so far. Other measures that have been applied to obtain reliefare bringing excess heat out of the appliance, by exhaling warm processair in exchange for cooler air and including additional heat exchangersto take excess heat from the heat transfer fluid by suitable additionalheat exchangers. All of these measures, however, introduce furthercomplexity and cost.

Details of GWP indices of generally known refrigerant compounds arelisted in the textbook “Solkane-Product Manual Refrigeration andAir-Conditioning Technology” by H. Buchwald, J. Hellmann, H. König, andC. Meurer, 2^(nd) ed. 08/2000. As to a quantitative classification ofrefrigerants in view of their flammabilities as expressed in a LowerFlammability Level index, reference is made to European Standarddocument IEC 60335-2-40, “Household and Similar ElectricalAppliances—Safety—particular Requirements for Electrical heat Pumps,Air-Conditioners and Dehumidifiers”, Edition 4.2 2005-07, Annex BB—TableBB.1. Pertinent information on refrigerants or heat transfer fluids isalso available in U.S. Standard ASHRAE 34, including a specificnomenclature for such compounds and a classification on security andtoxicity of such compounds.

The dryer disclosed in the Japanese abstract mentioned above has an openair conduit for process air which is taken into the dryer, heated by theheat pump's heat source, guided through laundry to be dried and tumbledin a rotating drum. Subsequently, the process air is guided through theheat pump's heat sink for cooling and recovering humidity from theprocess air by condensation. Finally, the process air is discharged fromthe dryer. While this dryer provides at least for a fraction of thehumidity extracted from the laundry to be recovered in liquid form, thedryer requires action by an operator to dispose of the liquid recovered.At any rate, this is unusual and may be disappreciated by an operatorbeing used not to care for disposal of any residual produced in a normallaundry dryer with an open process air conduit. In addition to theproblem of disposal of liquid residuals, the dryer as disclosed in theJapanese abstract will require a dedicated lint filter to remove fibrousor dust-like residuals, usually known as lint, from the process airexiting the laundry drum. Normal laundry will always release a quantityof lint upon drying by a flow of process air, that will precipitate onany guide structure or other component that is passed by the process aircarrying the lint and stick there due to the humidity precipitating fromthe process air concurrently. To avoid clogging of the heat sink bylint, a dedicated lint filter is needed to be placed upstream of theheat sink to catch as much lint as possible, and such filter will alsoneed attention by an operator to remove lint collected thereupon. Thiswill cause even more disappreciation of such dryer.

Accordingly, it is an object of the invention to specify a householdappliance as defined in the introductory chapter herein that has a heatpump which is detailed in a way so as to alleviate the problemsspecified above and allows for quicker drying of articles at anappropriate expense. In particular, it is an object of the invention tospecify a household appliance as defined above that avoids production ofcondensate liquid at least to a considerable extent. Likewise, it is anobject of the invention to specify a household appliance as definedabove that avoids the need for lint filtering.

The present invention provides a solution embodied in the householdappliance as defined in the independent claim. Preferred embodiments ofthe invention are defined in the dependent claims.

According to the invention, there is specified a household appliancecomprising a housing, a drying chamber for drying wet articles therein,a first air conduit for guiding process air drawn into said housing todry the articles and a heat pump, said heat pump comprising a heat sinkfor transferring heat into said heat pump, a heat source coupled to saidfirst air conduit for transferring heat from said heat pump into theprocess air, and a heat transfer device for transferring heat from saidheat sink to said heat source. Therein, said heat sink is coupled to asecond air conduit for guiding secondary air drawn into said housing,for transferring heat from the secondary air into said heat pump.

The present invention takes advantage from the fact that extracting heatfrom secondary air taken from the ambient of the appliance will ingeneral incur much less generation of condensate liquid than theextraction of heat from process air that is dedicatedly loaded withhumidity at or near a maximum capacity.

In addition, advantage is taken from the fact that the air taken intothe appliance from its ambient is cooler than the process air exitingthe drying chamber with the articles to be dried which will carry, as arule, at least a fraction of the thermal energy that had been loadedinto the process air by heating prior to its entering the dryingchamber. Accordingly, the invention provides for a defined leakage ofheat from the appliance that will balance against excess heat generatedby the heat pump due to fundamental laws of thermodynamics. Thereby, theinvention contributes to stabilizing the process of drying articles bybalancing generation of excess heat within the appliance withdissipation of heat from the appliance. This is of major importanceduring a major phase of the drying process, where any initial heat-up ofthe appliance and its components has been accomplished and the dryingprocess is desired to run in a quasi-stationary manner.

In addition as well, the process air is discharged from the applianceafter having flown through the drying chamber and around the articles tobe dried only once and possibly without passing any other functionallyactive component of the appliance. Accordingly, there is no considerabledanger of clogging by lint, and therefore, no dedicated lint filter isneeded in general. An exception may occur in case that a blower to drivethe process air is placed downstream of the drying chamber. Yet, aturbulent flow of process air through such blower may be expected, andsuch turbulent flow will prevent precipitation of lint within the blowerat least to a fair extent.

In accordance with a preferred embodiment of the invention, said heattransfer device comprises a heat transfer loop containing a heattransfer fluid to be circulated through said heat transfer loop, acompressor for compressing said heat transfer fluid and circulating saidheat transfer fluid through said heat transfer loop, and a nozzle fordecompressing said heat transfer fluid. Further, said heat sink isprovided to be an evaporator for transferring heat from the process airinto said heat transfer fluid by evaporating said heat transfer fluid,and said heat source is provided to be a liquefier for transferring heatfrom said heat transfer fluid to the process air by liquefying said heattransfer fluid. Accordingly, this heat pump is the known compressor-typeheat pump that is known in particular from cooling and freezingapplications, which fact provides for designating the heat transferfluid used in such heat pump commonly as “refrigerant”.

In accordance with a preferred embodiment that is a further developmentof the preferred embodiment defined just above, said heat transfer fluidcomprises a fluorinated hydrocarbon compound. In particular, said heattransfer fluid is selected from the group comprising refrigerants R134a,R152a, R290, R407C, and R410A.

While R134a and R152a are single fluorinated hydrocarbon compounds, R407C and R410A are mixtures of such compounds. R290 or propane in itsturn is an alkane or simple hydrocarbon compound. It has pertinentphysical properties that make it highly suitable for the applicationconsidered herein. In particular, propane has a GWP index of 3 that isremarkably low in comparison to a GWP index of 1300 for the conventionalheat transfer fluid R134a. Of course, application of propane which ishighly flammable will require dedicated protection of the system againstfire hazard. In order to combine a somewhat reduced flammability levelwith a fairly low GWP index, R152a is a particularly preferred choice.

In accordance with another preferred embodiment of the invention, saiddrying chamber is a rotatable drum.

In accordance with a further preferred embodiment of the invention, theappliance is configured as a dryer for drying wet laundry. Otherembodiments of the appliance according to this invention, namelyembodiments as a washer-dryer for both washing and drying laundry, or asa dishwasher, are considered.

In accordance with yet another preferred embodiment of the invention,said second air conduit is coupled to said heat transfer device fortransferring heat dissipated from said heat transfer device to saidsecondary air. This embodiment takes advantage of the presence of cooledsecondary air, which is applied to provide some cooling for componentsof the heat pump that drive the thermodynamic process and thus serve forentering additional energy which necessary to drive that process. Tothat end, it is more preferred that said second air conduit is arrangedfor the secondary air to pass said heat sink prior to passing said drivemeans. Yet more preferred said first air conduit and said second airconduit are combined into a single exhaust conduit for exhausting saidprocess air and said secondary air out of said housing. In suchembodiment, said exhaust conduit may comprise a single blower forexhausting said process air and said secondary air.

In accordance with yet a further preferred embodiment of the invention,said housing is open for an inflow of air into said housing, and saidsecond air conduit has an inlet disposed within said housing. With thesecond air conduit's inlet disposed within the housing, air which couldpick up some heat dissipated from components of the appliance includingthe drying chamber, the heat source, and parts of the first air conduit,is drawn into the second air conduit to be cooled down by the heat sink.As the heat extracted by the heat sink is returned to the drying processthrough the heat source, this returning of heat contributes to arecovery of dissipated heat and an according improvement of theefficiency of the drying process. Further, as air within the housingobtains a degree of preheating by dissipated heat, more advantage may beattained in case that the appliance is placed in a relatively coolambient. In such ambient, cooling secondary air drawn from the ambientmay lower the temperature of such secondary air below 0° C. and causeformation of ice at or around the heat sink. Such ice in turn may impairthe operational efficiency of the heat sink. A degree of preheating thesecondary air will mitigate any disadvantage of ice formation at leastto a considerable extent.

In accordance with again another embodiment of the invention, saidsecond air conduit has two inlets, whereof a first inlet is directedtowards said heat transfer device, and whereof a second inlet isdirected towards a motor for driving a first blower disposed in saidfirst air conduit and a second blower disposed in said second airconduit. Thereby, heat dissipated by two principal sources is recoveredby drawing air from the vicinities of these sources into the second airconduit. Even more preferred, said drying chamber is a rotatable drum tobe rotated by said motor. Thereby, only one motor is provided to drivethe movable components of the appliance except the heat transfer device,which contributes to a focused generation of excess heat which may inturn be recovered by means focused accordingly. A preferred example forsuch focused means is, in accordance with a yet more preferredembodiment, defined by said second blower being a two-flow blower havingtwo flows, and each inlet being disposed at a respective one of theseflows.

In accordance with still a further preferred embodiment of theinvention, the appliance comprises a bypass conduit connecting saidfirst air conduit and said second air conduit and switching means forselectively routing a fraction of said process air into said second airconduit through said bypass conduit. More preferred, said bypass conduitis connected to said first air conduit between said heat source and saiddrying chamber, and said bypass conduit is connected to said second airconduit upstream of said heat sink. Yet more preferred, the appliancecomprises a temperature sensor to detect a temperature at said heatsink, and a control device connected to said temperature sensor and saidswitching means. Further, said control device is arranged to engage saidswitching means for routing the fraction of said process air into saidsecond air conduit upon condition that the temperature detected by saidtemperature sensor is lower than a predefined limit temperature. Yetmore preferred, the appliance comprises a condensate sensor disposed insaid second air conduit, said condensate sensor linked to said heat sinkto detect condensate formed at said heat sink, with said control deviceconnected to said condensate sensor and said heat pump, and said controldevice being arranged to operate said heat pump in response todetections received from said condensate sensor. Still more preferred,said control device is connected to a drive means comprised by said heatpump, and said control device is arranged to operate said heat pump byoperating said drive means.

The appliance including such bypass conduit may adapt its modes ofoperation to a variety of ambient an operating conditions. In case ofvery low ambient temperature, the flow of secondary air could be mixedwith a fraction of the process air branched off upstream of the dryingchamber, in order to avoid predominantly low temperatures of process airpassing the heat sink which might cause a formation of ice at the heatsink which would constrict the second air conduit and impair operationof the heat pump. Further, the bypass conduit can be used to perform ade-icing operation, during which operation of the heat pump would be cutoff, and process air after diverted into the bypass conduit after havingpassed the heat source, to pass the heat sink to melt ice formed there.Such de-icing operation can also be used to provide some preheating ofthe heat sink prior to starting a drying process, by guiding warmprocess air diverted through the bypass conduit past the heat sink. Suchwarm process air may be obtained by heating the process air with anadditional heater as specified hereinbelow. In addition to avoidingformation of ice within the appliance, the bypass conduit may also beused to prevent excessive formation of condensate at the heat sink asmay occur under relatively warm and humid ambient conditions. The samesecondary processes as specified just above may be used to control thetemperature at the heat sink to avoid excessive condensation.Application of these secondary processes may be controlled by a controldevice of the appliance and by use of dedicated sensors as specifiedhereinabove.

In accordance with again another preferred embodiment of the invention,the appliance comprises a heater disposed in said first air conduitupstream of said drying chamber, for selectively heating said processair.

The separate heater may be used to obtain quick pre-heating of theappliance during a heat up phase of operation, and may be applied toprovide for some additional heating during a steady phase of operation.Such additional heating may be practical in order to avoid formation ofice or excessive condensation at the heat sink when used concurrentlywith a bypass conduit, as specified just above.

Exemplary preferred embodiments of the invention are now described indetail, with reference to the accompanying drawing. The drawingcomprises schematic figures of household appliances. In particular,

FIG. 1 shows a first embodiment of a household appliance;

FIG. 2 shows an arrangement of components of a second embodiment of ahousehold appliance;

FIG. 3 shows an arrangement of components of a third embodiment of ahousehold appliance; and

FIG. 4 shows some features of a fourth embodiment of a householdappliance

FIG. 1 shows a household appliance 1 which comprises a housing 2 thatcontains all components of the appliance 1 to be described herein belowand that is disposed in a suitable household ambient. The appliance 1further comprises a drying chamber 3 that is provided in the form of adrum 3 rotatable around an axis of rotation 4. The drum 3 may beaccessed by door 5, for charging with articles 6 to be dried in form ofhumid laundry 6. After being dried, the laundry 6 may be dischargedthrough door 5 as well.

For the purpose of drying the laundry 6, air is drawn into the appliance1 through first air conduit 7 by a first blower 8 that is operable bymotor 9. To prevent dust and other dirt from contaminating the laundry6, a filter 10 is provided in the first air conduit 7. Process air beingdrawn through the first air conduit 7 may be heated by electric heater11. Electric heater 11 may be replaced by a heater operated bycombustion of liquid or gaseous fuel in accordance with pertinentknowledge in the field of laundry dryers. In the present case, heater 11is only an accessory component; the main share of the heating of theprocess air is accomplished by a heat pump 12, 13, 14, 15, 16, 17 whichcomprises a heat source 13 that forms a part of the first air conduit 7.In accordance with pertinent knowledge, the appliance 1 may be specifiedto be an exhaust-type laundry dryer, because process air that isconveyed through first air conduit 7 is guided in an open cycle, bybeing drawn to the appliance 1 through first air conduit 7, passing thearticles 6 only once and being exhausted from the appliance 1subsequently.

The heat pump 12, 13, 14, 15, 16, 17 comprises besides the heat source13 and the heat sink 14 that is coupled to a second air conduit 18, aheat transfer device 12, 15, 16, 17 comprising a heat transfer loop 12containing a heat transfer fluid that is circulated by a compressor 15driven by a compressor motor 16, and a nozzle 17. For operation of suchheat pump 12, 13, 14, 15, 16, 17, reference may be made to pertinentknowledge of persons skilled in the art. Anyway, the heat transfer fluidwhich may be one of refrigerants R134a, R152a, R290, R407C, and R410A,will enter heat sink 14 in liquid form, to be evaporated by taking upheat from secondary air flowing through second air conduit 18 that theheat sink 14 belongs to. After vaporization in the heat sink 14, theheat transfer fluid will flow through compressor 15, which compressesthe heat transfer fluid to increase both its internal pressure and itstemperature. Subsequently, the compressed heat transfer fluid enters theheat source 13 and is liquefied there, by releasing heat to the processair flowing through the first air conduit 7. Upon exiting the heatsource 13, the heat transfer loop 12 guides the liquefied heat transferfluid through a nozzle 17, where the internal pressure of the liquidheat transfer fluid is reduced. The nozzle 17 is to be understood as arepresentative for a plurality of suitable means including the nozzle 17in its proper form, a capillary and a check valve. Downstream of thenozzle 17, the liquid heat transfer fluid with reduced internal pressureis guided back to the heat sink 14 to complete its cycle through theheat transfer loop 12. Accordingly, by operation of the heat pump 12,13, 14, 15, 16, 17, process air flowing through the first air conduit 7is heated by heat extracted from secondary air flowing through thesecond air conduit 18. Accordingly, it is heat extracted from theambient of the appliance 1 which is transferred into the process air forthe purpose of heating to dry the laundry 6 contained in the drum 3.

It may be noted that the heat pump shown in FIG. 1 and the subsequentfigures should be regarded as a representative of other configurationsthat may be applied to transfer heat from the secondary air to theprocess air, examples of such configuration being part of pertinentknowledge. As examples, thermoelectric heat pumps and adsorption-typeheat pumps may be mentioned besides others.

The second air conduit 18 has an inlet 19 that is not directly open tothe appliance's 1 ambient. Rather, the inlet 19 is disposed within thehousing 2, for air from inside the housing 2 to be drawn into the secondair conduit 18. The housing 2 in turn has openings 20 in the form ofsmall slits 20 or the like, which allow air from the ambient of theappliance 1 to enter the housing 2 and replace air that has been drawninto the second air conduit 18. The advantage of this configuration hasbeen explained in detail hereinabove, the basic point being to takeadvantage of heat dissipated into such air from the drum 3, the firstair conduit 7 and the heat source 13.

As the heat sink 14 provides for a considerable cooling of the secondaryair, condensation of humidity contained in such secondary air at theheat sink 14 must be expected. Accordingly and in conformance withpertinent knowledge, heat sink 14 is designed in such a way to allow forcollection of such condensate and guiding such condensate to acondensate collector 21 for disposal after completion of a dryingprocess.

The second air conduit 18 comprises a cooler portion 22 that is arrangedin operative connection to the compressor 15 and the compressor motor16, to provide for some cooling of these components. By such cooling,accumulation of excess heat within the heat transfer loop 12 can beavoided, and stable operation of the heat transfer loop 12 assured.

The first air conduit 7 and the second air conduit 18 are combined intoa single exhaust conduit 23 downstream of the drum 3 and the coolerportion 22, respectively. First blower 8 is disposed within the exhaustconduit 23, to draw both the process air through the first air conduit 7and the secondary air through the second air conduit 18 simultaneously.

To provide for a degree of control of the operation of the appliance 1,a temperature sensor 24 is placed at the heat sink 14 to detect a localtemperature at the heat sink 14. Likewise, a condensate sensor 25 isplaced at the condensate collector 21 to allow for monitoring thegeneration of condensate at the heat sink 14. By these sensors 24 and25, operation of the heat sink 14 may be controlled to avoid undesirablylow temperatures at the heat sink 14 which might cause the formation ofice within the second air conduit 18. Temperature sensor 24 may beapplied to monitor the temperature of the heat sink 14 directly, and thecondensate sensor 25 may be used to monitor the operating condition ofthe heat sink 14 indirectly via an assessment of condensate producedduring operation of the appliance 1. Details have been specifiedhereinabove. It should be noted that the sensors 24 and 25 shown are notmeant to be the totality of sensors present in the appliance 1 and usedto provide full control of its operation. Reference is made to pertinentknowledge for further sensors that may be used, in particular forsensors within the first air conduit 7, to monitor temperatures of thelaundry 6 and thus control operation of the appliance 1. Anyway, suchcontrol is exercised by the control device 26 which is connected to alloperative an controllable components of the appliance 1 throughconnection lines 27 for power supply or for reception of signals, as maybe the case.

FIG. 2 shows a development of the embodiment from FIG. 1, with onlythose components shown which are important in the present context. Itmay be noted that in this embodiment the second air conduit 18 draws airnot from within the housing 2, but directly from the ambient of theappliance 1. Of major importance is the bypass conduit 28 that connectsthe first air conduit 7 and the second air conduit 18, and branches offfrom the first air conduit 7 downstream of the heat source 13, inparticular even downstream of the heater 11 but upstream of the drum 3.Accordingly, the bypass conduit 28 allows conveying a fraction of theprocess air into the second air conduit 18 after heating up by the heatsource 13 and the optional heater 11. This has the advantage that anundesirably low temperature at the heat sink 14 and monitored bytemperature sensor 27, for example, can be avoided by rising thetemperature of the secondary air at the heat sink 14. Likewise, the heatsink 14 and neighbouring portions of the second air conduit 18 may bepre-heated during a heat up phase of the drying process, by operatingthe switching device 29 (exemplified as a flap 29) at the bypass conduit28 to shut off the second air conduit 18 from its normal inlet 19, todraw only air which has been heated up by the heat source 13 and/or theheater 11. Such pre-heating may also be performed during a steady phaseof a drying process; in such circumstance, normal operation of the heatpump 12, 13, 14, 15, 16, 17 should be discontinued to avoid furthercooling at the heat sink 14, but heated air being still obtainable atleast for a while by making use of residual heat contained in the heatsource 13. By any method specified here or hereinabove, the bypassconduit 28 can be very useful to avoid undesirable operating conditionsat the heat sink 14. Of course, the embodiment shown in FIG. 2incorporates as well a control device 26, to operate the variouscomponents mentioned here through appropriate connecting lines 27.

FIG. 3 shows an alternative embodiment of the appliance 1, which ischaracterized by keeping the first air conduit 7 and the second conduit18 separate from each other. It should be noted that this embodiment maybe further developed by incorporating a bypass conduit 28 and aswitching device 29 as shown in FIG. 2. As to the first air conduit 7,it should be noted that an exhaust hose 30 is connected to the outlet 31of the first air conduit 7. As a rule, process air that is exhaustedfrom the first air conduit 7 will contain a considerable amount ofhumidity. Accordingly, such process air should not be exhausted into theimmediate ambient of the appliance 1, to avoid precipitation of suchhumidity in that ambient. In case of an appliance 1 placed within abuilding, it is common practice to provide some guide through which suchprocess air can be conveyed out of the building. Such guide in turn willnormally include a more or less flexible hose 30 for connection to theappliance 1. Of course, such hose 30 should also be considered whenplacing an appliance 1 as shown in FIG. 1 or FIG. 2 within a building.

As the second air conduit 18 is at least in principle separate from thefirst air conduit 7, the second air conduit 18 includes a separatesecond blower 32 to drive the secondary air there through. It should benoted that it may be desirable to drive both blowers 8 and 32 by asingle motor 9 as shown in FIG. 1. It should also be noted that thecooler portion 22 of the second air conduit 18 is embodied as anenclosure wherein the drive means 15 and 16 of the heat pump 12, 13, 14,15, 16, 17, in particular the compressor 15 and the compressor motor 16,are disposed.

FIG. 4 shows some exemplary details of the household appliance 1,namely, some components disposed on a bottom portion thereof. Theappliance 1 has a housing 2 and comprises, disposed within that housing2, all of its functional components including a first air conduit 7, afirst blower 8 disposed therein, a motor 9 and various other componentsincluding some that belong to the heat pump 12, 13, 14, 15, 16, 17: aheat source 13 that, in this case, defines also an inlet of the firstair conduit 7, a heat sink 14 disposed in a second air conduit 18, and acompressor 15. First blower 8, made in the form of a single-flow radialblower, conveys process air upwards to a drum 3 (see other figures)disposed above the arrangement shown in FIG. 4 after heating by heatsource 13. After passing the drum 3 and wet laundry disposed therein fordrying, the process air returns to a portion of the first air conduit 7located in the upper right portion of FIG. 4, and exits the appliance 1through exhaust conduit 23. The second air conduit 18 has two inlets 19which are located at respective inlets of the second blower 32 which isformed as a two-flow radial blower with two inlets at opposing sides.Thereby, second blower 23 may draw secondary air both from a vicinity ofcompressor 15 and from a vicinity of motor 9 that, through a singledriving shaft 33, drives both the first blower 8 and the second blower32. This configuration gives the advantage that excess heat from thecompressor 15 as well as excess heat from the motor 9 is removed throughthe second air conduit 18, with the further benefit that the secondaryair to be cooled in the heat sink is given some initial heating that mayprevent an excess of liquid condensate or even ice from forming in theheat sink 14. After passing the heat sink 14, the secondary air isguided into the exhaust conduit 23 where it may merge into the processair. To provide further simplicity and according benefit, motor 9 isalso scheduled to drive the drum 3 by a belt that is slung both aroundthe drum 3 and a driving wheel 34 disposed on the driving shaft 33.

At any rate, the appliances shown in detail herein are characterized byincorporating recovery of heat used in a drying process at least to aconsiderable extent, while retaining all pertinent positive features ofnormal exhaust-type appliances designed for drying.

LIST OF REFERENCE NUMERALS

-   1 Household appliance, dryer-   2 Housing-   3 Drying chamber, drum-   4 Axis of rotation-   5 Door-   6 Wet articles, laundry-   7 First air conduit-   8 First Blower-   9 Motor-   10 Filter-   11 Heater-   12 Heat transfer device, heat transfer loop-   13 Liquefier, heat source-   14 Evaporator, heat sink-   15 Heat transfer device, compressor-   16 Heat transfer device, compressor motor-   17 Heat transfer device, nozzle-   18 Second air conduit-   19 Inlet of second air conduit-   20 Slit in housing-   21 Condensate collector-   22 Cooler Portion-   23 Exhaust conduit-   24 Temperature sensor-   25 Condensate sensor-   26 Control device-   27 Connection line-   28 Bypass conduit-   29 Switching means, flap-   30 Exhaust hose-   31 Outlet of first air conduit-   32 Second blower-   33 Driving shaft-   34 Driving wheel

1-20. (canceled)
 21. A household appliance, comprising: a housing; adrying chamber to dry wet articles in the drying chamber; a first airconduit to guide process air drawn into the housing to dry the wetarticles; a heat pump, including: a heat sink to transfer heat into theheat pump; a heat source coupled to the first air conduit to transferthe heat from the heat pump into the process air; and a heat transferdevice to transfer the heat from the heat sink to the heat source; and asecond air conduit coupled to the heat sink to guide secondary air drawninto the housing, the heat sink to transfer the heat from the secondaryair into the heat pump.
 22. The household appliance of claim 21, whereinthe heat transfer device comprises: a heat transfer loop containing aheat transfer fluid that circulates through the heat transfer loop; acompressor to compress the heat transfer fluid and to circulate the heattransfer fluid through the heat transfer loop; and a nozzle todecompress the heat transfer fluid; wherein the heat sink is anevaporator to transfer the heat from the process air into the heattransfer fluid by evaporating the heat transfer fluid; and wherein theheat source is a liquefier to transfer the heat from the heat transferfluid to the process air by liquefying the heat transfer fluid.
 23. Thehousehold appliance of claim 22, wherein the heat transfer fluidcomprises a fluorinated hydrocarbon compound.
 24. The householdappliance of claim 22, wherein the heat transfer fluid is selected fromthe group consisting of refrigerants R134a, R152a, R290, R407C, andR410A.
 25. The household appliance of claim 21, wherein the dryingchamber is a rotatable drum.
 26. The household appliance of claim 21,wherein the household appliance is a dryer for drying wet laundry. 27.The household appliance of claim 21, wherein the second air conduit iscoupled to the heat transfer device for transferring the heat dissipatedfrom the heat transfer device to the secondary air.
 28. The householdappliance of claim 27, further comprising drive means, wherein thesecond air conduit is arranged such that the secondary air passes theheat sink prior to passing the drive means.
 29. The household applianceof claim 27, wherein the first air conduit and the second air conduitare combined into a single exhaust conduit for exhausting the processair and the secondary air out of the housing.
 30. The householdappliance of claim 29, wherein the single exhaust conduit comprises asingle blower for exhausting the process air and the secondary air. 31.The household appliance of claim 21, wherein the housing is open for aninflow of air into the housing, and wherein the second air conduit hasat least one inlet disposed within the housing.
 32. The householdappliance of claim 31, further comprising: a first blower disposed inthe first air conduit; a second blower disposed in the second airconduit; and a motor to drive the first blower and the second blower;wherein the at least one inlet includes a first inlet and a secondinlet; wherein the first inlet is directed towards the heat transferdevice; and wherein the second inlet is directed towards the motor fordriving the first blower disposed in the first air conduit and thesecond blower disposed in the second air conduit.
 33. The householdappliance of claim 32, wherein the drying chamber is a rotatable drumthat is rotated by the motor.
 34. The household appliance of claims 32,wherein the second blower is a two-flow blower having two flows, andwherein each of the first inlet and the second inlet is disposed at arespective one of the two flows.
 35. The household appliance of claim21, further comprising: a bypass conduit connecting the first airconduit and the second air conduit; and switching means for selectivelyrouting a fraction of the process air into the second air conduitthrough the bypass conduit.
 36. The household appliance of claim 35,wherein the bypass conduit is connected to the first air conduit betweenthe heat source and the drying chamber, and wherein the bypass conduitis connected to the second air conduit upstream of the heat sink. 37.The household appliance of claim 35, further comprising: a temperaturesensor to detect a temperature at the heat sink; and a control deviceconnected to the temperature sensor and the switching means; wherein thecontrol device is configured to engage the switching means for routingthe fraction of the process air into the second air conduit when thetemperature detected by the temperature sensor is lower than apredefined threshold temperature.
 38. The household appliance of claim37, further comprising a condensate sensor disposed in the second airconduit, wherein the condensate sensor is linked to the heat sink todetect condensate formed at the heat sink; wherein the control device isconnected to the condensate sensor and the heat pump; and wherein thecontrol device is configured to operate the heat pump in response todetections received from the condensate sensor.
 39. The householdappliance of claim 38, further comprising drive means that include theheat pump, wherein the control device is connected to the drive means,and wherein the control device is structured to operate the heat pump byoperating the drive means.
 40. The household appliance of claim 21,further comprising a heater disposed in the first air conduit upstreamof the drying chamber for selectively heating the process air.